How to slope floor for drain in Sauna

To all,

I've built a 7x10' sauna off the ground and plan on putting a drain in the center of one of the 7' walls. The floor is level and plywood. How do I go about creating a gradual slope across the room and direct water to the drain? I am planning on installing tile and was trying to determine if I could use cement board to create the floor or would I need to attempt to pour a floor?